Cathode-ray beam deflecting circuits



C. H. SCHADE CATHODE RAY BEAM DEFLECTING CIRCUITS Filed June 30 1945 ATTOBNK Lw/f6 1N VEN TOR. an@ H. Salad@ BY May 4, 1948.

"ETL- mtl occur and in order that the dimensions of Patented May 4g,i948 2,440,186 cA'rHonE-RAY BEAM DEFLECTING CIRCUITS Otto H. Schade,West Caldwell,.N. J.. assignor tov Radio Corporation of America,

Delaware a corporation of Application .lune 30, i943, Serial No. 492,868

(Cl. F75-335) 2 Claims.

This inventionrelates to an improvement in cathode ray beam defiectingcircuits, and more particularly, in circuits used forelectromagnetically deflecting acathode ray beam in such a manner that ahigh degree of linearity of deflection and stability of amplitude ofdeflection may be maintained.

Where a cathode ray tube is used to produce luminous indications, it isfrequently desirable to deflect the cathode ray beam in the tube at apredetermined constant rate of speed across the screen of the tube. Thisis'particularly true in the case of television receivers where thelinearity of deection should be maintained at the highest possibledegree in order that no distortion will be present in the producedtelevision picture. It is also desirable that the degree of deflectionor the deection amplitude be maintained constant in order thatdistortion will not the produced image will not be altered.

It is well known that a cathode ray beam may be deflected byelectrostatic or electromagnetic fields, and the latter form ofdeflection is the type with which the present invention is concerned.

Various circuit arrangements have been provided for improving thelinearity of beam deection in electromagnetic deflection circuits, butin most instances true linearity is not completely obtained, with theresult that the rate of deflection of the cathode ray beam across thescreen is not absolutely uniform throughout the entire deectioninterval.

By means of the present invention, a circuit arrangement has beenprovided whereby a high degree of linearity maybe accomplished in acathode ray beam deection circuit. It is also possible by means of thepresent invention to maintain the amplitude of deflection substantiallyconstant irrespective of changes in operating conditions and variationsin the voltages applied to the tubes as may occur in normal operation ofthe system.

The purposes of the present invention are in general accomplished byutilizing degenerative feedback in the deflection system, the systemhaving inherently relatively small wave form distortion, with the resultthat a very high degree of linearity of deflection will result. By thesame arrangement it is also possible to maintain the amplitude ofdeflection substantially constant in spite of operational drifts thatmay occur during the normal operation of the system. Through the use ofthe present invention, it is also possible to maintain a high degree oflinearity of deflection over a considerable range of frequencies, andaccordingly the present invention may be used in a wide variety ofapparatus wherein cathode ray tubes are employed.

The present invention may also be applied to deflection circuits whereinthe deflection tubes are operated in either class A or class B.

It is, therefore, one purpose of the present invention to provide acircuit for electromagnetically deflecting a cathode ray beam in which ahigh degree of linearity of deflection may be maintained.

Another-:purpose of the present invention resides in the provision of acircuit for electromagnetically deflecting a cathode ray beam in whichthe amplitude of deflection may be maintained substantially constantirrespective of normal operational changes in the system.

Still another purpose of the present invention resides in the provisionof a circuit for electromagnetically deecting a cathode ray beam inwhich a high even though low percentages of harmonic distortion mayoccur in the various tubes used in the deflection circuit.

Still another purpose of the present invention resides in the use ofdegenerative feedback in a circuit for electromagnetically defiecting acathode ray beam thereby to improve the linearity of deection and tomaintain the amplitude of deflection stable.

A still further purpose of the present invention resides in theapplication of degenerative feedback in a cathode ray beam deflectingcircuit where the-deiection tubes are caused to function in either classA or class B operation.

Still another purpose of the present invention resides in the provisionof means in a circuit for electromagnetically deiecting a cathode ra?beam wherein a potential drop is produced as a result ofthe ow of thebeam deflection current, the produced potential drop being utilized in adegenerative manner to improve linearity of deection and to maintain theamplitude of deection uniform.

Various other purposes and advantages of the present invention willbecome more apparent to those skilled in the art from the followingdethe drawings, and particdegree of linearity'is produced ularly toFigure 1 thereof, there is shown an electron discharge tube I whichincludes a, cathode, a control electrode and an anode. The cathode oftube I IJ is connected directly to ground or a point of fixed potential,whereas the control electrode is connected to one of the input terminalsI2 in order that a voltage variation of the desired wave form may beapplied thereto. The anode of tube -l0 is connected,l by way of loadresistor l'6, to positive terminal I4 (to which a source of positivepotential is applied). The anode of tube I0 is also connected to groundby way of a resistance-capacitance circuit including resistance I8,coupling condenser 20 and a further condenser 22. The two condensers 20and 22, as well as the resistance I 8, are connected in seriesto formthe resistance-capacitance circuit.

The control electrode of tube ID issupplied with a, series of negativeimpulses, as represented by the curve 24 in the drawing. These impulsesoccur at a frequency corresponding to the desired deflection frequency.Tube I0 is normallyv conducting, but is intermittently renderedsubstantially non-conducting by the succession of negative impulsesapplied to the control electrode thereof. During thesel non-conductingintervals, the series condensers and 22 are charged through resistancesI6 and I8, and are subsequently discharged by the tube I 0 during itsconducting intervals. As a result, a voltage Variation is produced atthe junction of the series condensers 20 and 22 similar to thatrepresented by the curve 26.

The resistance-capacitance circuit forms an integrating circuitresponsive to the potential variations at the anode of tube IIJ, thesepotential variations corresponding to the applied pulse series 24 exceptthat their polarity is reversed. The capacitance 20 should preferably bechosen to have a value equal to about twice the capacitance of thecondenser 22. With such an arrangement the linearity of the sawtoothshaped .voltage variations 26 present at the junction of the condensers2D and 22 can be made very good if only a relatively small percentage ofthe full anode voltage is used.

'I'he voltage variation represented by the curve 26 is applied to thecontrol electrode of tube 36, which includes at least a cathode, acontrol electrode and an anode, but Which is preferably of the screengrid type. The cathode 32 of the tube 30 is connected to ground by wayof cathode resistance 34, and the anode of tube 30 is connected to thepositive terminal I4 by Way of anode load resistance 36. When thepotential of the control electrode of tube 30 is varied by the voltagevariation appearing at the junction of condensers 20 and 22, acorresponding voltage Variation of sawtooth wave form will be producedat the anode of tube 30, as indicated by the curve 39. These voltagevariations are then applied to the control electrode of a powerdeflection tube 40 by way of coupling condenser 38. The controlelectrode of tube 40 is connected to ground by way of grid resistor 42.The cathode of tube 40 is connected to ground by way of cathoderesistance 44, in order that the potential drop thereacross will producethe desired relative potential between the cathode and control electrodeof the tube. It is preferable that some degeneration be present in thetube and, as a result, no by-pass condenser is connected in parallelwith the cathode resistance 44.

The power deflection tube 40 is preferably of the beam power type, andincludes a cathode, control electrode, screen electrode and anode. Thescreen electrode may be connected directly to the positive terminal I 4,whereas the anode of tube 40 is connected to the positive terminal byway of the primary winding 46 of transformer 48. A damping resistance 50and condenser 52 are connected in series across the primary winding 46of the transformer. The transformer 48 is also provided with a secondarywinding 54, one terminal of which is connected to ground, and the otherterminal of which is connected to a contact point 56. The anode of tube40 is connected to another contact point 58. and switch arm 60 isprovided for cooperating selectively with one or the other of contactpoints 56 or 58.

The dellecting coil or coils 62 for electromagnetically dellecting thecathode ray beam are then connected between the movableY switch arm 6Uand the cathode of tube 30, with condenser 64 interposed in the cathodeconnection. By means of the switch arm 6D, the deiiecting coil 62 maythen be energized directly from the anode of tube 40, or it may beenergized through the transformer 48 from the voltage induced in thesecondary winding 54.

When voltage variations of sawtooth wave form, such as represented bythe curve 39, are applied to the control electrode of tube 40, thedesired current variation in the anode circuit of tube 4|] is producedsuch that substantially linear deflection of the cathode ray beamresults.

By reason of the fact that the deflection coil current flows through theresistance 34 in the cathode circuit of tube 30, a negative feedbackvoltage is produced by a corresponding potential drop across resistance34. Accordingly, the current in the plate circuit of tube 30 is affectedboth by the voltage variations applied to the control electrode of tube30 and by variations in the potential drop across the cathode resistance34. These two voltages add in phase but with opposing polarity, i. e.,in a degenerative sense. When degenerative feedback is provided in thismanner, the circuit shown in Figure 1 will operate to deflect thecathode ray beam at substantially any scanning frequency, and a highdegree of linearity of deflection will result. Furthermore, theamplitude of deflection will be main*- tained substantially constant.

For most efficient operation, it is desirable that the system inherentlyhave good linearity since departure from' strict linearity, whencorrected by degeneration, can only be improved by the same percentageas the gain or degree of amplication is reduced. In order, therefore, tonot excessively reduce the gain of the deflection system, it ispreferable that the system have inherently fairly good linearity so thata minimum amount of degenerative reaction is necessary in order` thatthe desired high degree of linearity of deflection may be accomplished.

Before feedback can be effective to reduce or compensate for distortion,it is necessary that the tube into which the feedback voltage isinjected, as well as all tubes following that tube, be in an operatingcondition during the time that the feedback is to be effective.Accordingly, if the degenerative feedback shown in Figure 1 is to beeffective over the entire deection stroke, then it is necessary thattubes 30 and 40 be operated in class A operation. When class AB or classB operation is employed, i. e., when the tube is inoperative during aportion of the cycle, naturally the tube is inoperative during thecut-off period and hence cannot reduce distortion during this period.The circuit shown in Figure l, therefore?, employs tubes with class YAoperation, and when degenerative feedback is employed such as shown inthe figure, a high degree of linearity of deflection may be maintainedand the degree or amplitude of deilection may be held substantiallyconstant.

A modification of the present invention is shown in Figure 2 in which amodified form of degenerative feedback is employed. In this circuit, atube is provided having at least a cathode, a control electrode and ananode, the tube being preferably of the beam power type. A condenser 12is provided, one plate of which is connected to input terminal 16, theother plate being connected to ground -by way of an adjustableresistance 16. Thecondenser 12 is the discharge condenser on which arising sawtooth voltage is generated from a preceding tube (not shown),so that a voltage variation of substantially sawtooth wave form. asrepresented by curve 15, is present at the input terminal 1B, and thisvoltage variation is applied 'to thevcontrol electrode of tube 10 by wayof coupling condenser 18. The control electrode of tube 10 is connectedto ground by grid resistor 80, and the cathode of tube 10 is alsoconnected to ground by cathode resistance 82, this resistance beingby-passed by condenser 89.

The anode of tube 10 is connected to a positive terminal 86 (to which asource of positive potential is applied) by way of series connectedinductance 88 and resistance 90. The resistance 90 has 'a valuegenerally several times the resistance of the deec'ting coils, and maybe eliminated if the resistance of the choke coil 88 is suillcientlyhigh. The defiectng coils 92 for electromagnetically deflecting thecathode ray beam are connected between the anode of tube 10 and thejunction of condenser 12 and resistance 16 by way of a condenser 96.This condenser 94 is preferably of relatively large capacity and may beof the electrolytic type.

A controlled damping tube or inverted tube 96 is also employed, and thistube includes at least a cathode, a control electrode and an anode. Thecathode of tube 96 is connected directly to the anode of tube 10, whilethe anode of tube 96 is connected to the positive terminal 86 by way ofadjustable resistance or potentiometer 98. The anode of tube 96 is alsoconnected to a single-pole double-throw switch |00 in order that theanode may be connected selectively (1) to the junction of condenser 94and defiecting coils 92, and thence to resistance 16 by way of lowalternating current impedance or condenser 94, or (2) to ground by wayof condenser |02.

The tube 96 is preferably of the beam power type, in which case it alsoincludes a screen electrode to which an adjustable potential may beapplied by means of the potentiometer |04. The resistance element ofthis potentiometer is connected between the positive terminal 86 andground, and the movable contact of the potentiometer is connected to thescreen electrode by resistance |06. A decoupling condenser |08 isconnected between the screen electrode and ground.

The control electrode of tube 96 is connected to its cathode by means oftwo series connected parallel resistor-condenser combinations, the rstof which includes resistance |0| and condenser H2, and the second ofwhich includes resistance H4 and condenser IIS.

With the circuit arrangement as described,

when a voltage variation of sawtooth wave form is applied to the controlelectrode of the tube 10, a current variation is produced in thedeecting coils to electromagnetically deflect the cathode ray beam in asubstantially linear fashion. Inasmuch as a portion of the current inthe defiecting coils, depending on the position of switch |00, must flowthrough the resistance 10, a potential drop is produced thereacrosswhich is also effective to modulate the potential of the controlelectrode of tube 10. This provides degenerative feedback which is fullyeil'ective and caused by the currents of tube 10 and. tube 96 when theswitch arm |00 is connected to the condenser |02. The resistance 0|serves then as an isolation resistor, providing a direct current pathfor the beam centering current. The resistor |0| may be replaced by anappropriately chosen choke. Partial feedback results when the switch arm|00 is moved into contact with the junction ofl the deilecting coils 92and the condenser 94 (as shown ,y

tions is shown and described, for example, inV

Schade U. S. Patent No. 2,382,822, `issued on August 14, 1945. Linearityof the deection can in part be controlled by the potentiometer |04,since an adjustment of this potentiometer determines the amount ofcurrent permitted to passv through tube 96. The adjustable resistance 98is effective for centering the cathode ray beam on the screen.

The degree of degeneration or inverse feedback can be regulated by anadjustment of resistance 16 since an increase in the size or value ofresistance 16 naturally increases the degree of degeneration. If thedegree of degeneration is increased, the amplitude of deiiection isdecreased, with the result that a variation in size of the scannedraster may be controlled by varying the value of the resistance 16.Conversely, if the value of resistance 16 is decreased, the degree ofdegeneration is decreased and the size or amplitude of deflection iscorrespondingly increased.

Accordingly, by reason of the particular circuit arrangements and thedegenerative feedback provided therein, it is possible to maintainexcellent linearity for very large deflection size or amplitudevariations. This is a result which has heretofore been difdcult, if notimpossible, to achieve. When the potentiometer |04 is properly adjustedto produce good linearity without feedback, a very high degree oflinearity and stability may then result by reason of the degenerativecfeedback, and the degree oi degenerative feedback may then be utilizedto control the size or amplitude of deection.

Since a damping or controlled inverted tube 96 is included in thecircuit shown in Figure 2, it is possible that tube 10 may be operatedas class AB if desired, although the circuit arrangement shown anddescribed is most effective for class A operation of the tube.

Although the circuits shown in Figures 1 and 2 have been describedsomewhat indetail. it is Having nowdescribed my invention, what I Iclaimas new and desire to have protected by Letters Patent is:

1. A cathode ray beam deecting Icircuit cornprising means for generatinga voltage variation .of substantially saw tooth Waveform, an electrondischarge tube having at least a cathode, a control electrode and ananode, means 'including an impedance for maintaining the anode positivewith respect to the cathode, a grid resistance for connecting thecontrol electrode to a point of fixed potential, a condenser and anadjustable resistance connected in series between the control electrodeand the point of fixed potential, means to apply the generated voltagevariation oft' saw tooth waveform to the control electrode of said tubeto produce corresponding potential variations at the anode thereof, acathode ray beam deiecting coil, means to couple the cathode ray beamdeecting coil to the anode of said tube so that current variations willbe produced therein in response to the potential variations present atthe anode of said tube, an inverted discharge tube effectively connectedin parallel with the deiiecting coil, and means including a condenser todirect at least a portion of the deflecting coil current variationsthrough the adjustable resistance associated with the control electrodeof said tube whereby a potential variation will b`e produced across saidadjustable resistance, the potential variations being in phase with thegenerated voltage variations of saw tooth waveform and having a polarityopposite to that of the generated voltage variations.

2. A cathode ray beam deflecting circuit comprising means for generatinga voltage variation of substantially saw tooth waveform, a deflectionpower tube having at least a cathode, a control electrode 4and an anode,means including an impedance to maintain the anode positive with respectto the cathode, means including a resistance to connect the controlelectrode of said tube to a point of xed potential, a condenser and anadjustable resistance connected in series between the control electrodeand the point of fixed potential, means to apply the generated voltagevariations to the control electrode of said tube to producecorresponding voltage variations at the anode thereof, a cathode raybeam deflecting coil, means including said adjustable resistance toconnect the deflecting coil between the anode off said tube and thepoint of fixed potential so that current variations are produced in saiddeilecting coil and in said adjustable resistance in response to thevoltage variations at the anode of said tube, an electron discharge patheil'ectively connected in parallel with said deflecting coil, and meansto alter the impedance of the electron discharge path in accordance withthe waveform of the potential variation at the anode of the deflectiontube, the potential variations caused 'by the current variations in saidadjustable resistance being effective to modulate the potential of thecontrol electrode of said deflection tube, the potential variationsbeing in phase with and degenerative with respect to the degeneratedvoltage variations of substantially saw tooth waveform.

OTTO H. SCHADE.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number l Name Date 1,519,211 Martin Dec. 16, 19241,925,160 Whitelock Sept. 5, 1933 2,085,409 Bedford June 29, 19372,147,114 Stocker Feb. 14, 1939 2,167,368 Meyers July 25, 1939 2,168,403Geiger Aug. 8, 1939 2,241,762 Blumlein May 13, 1941 2,251,851 Moore Aug.5, 1941 2,254,031 Faudell Aug. 26, 1941 2,280,733 Tolson Apr. 21, 1942FOREIGN PATENTS Number Country Date 424,221 Great Britain Feb. 18, 1935515,158 Great Britain Nov. 28, 1939 OTHER REFERENCES Radio Engineering,by F. E. Terman, 2nd ed., 3rd impression, 1937, published by McGraw-HillBook Co., Inc., pages 253, 254 and 255.

Radio Engineers Handbook, by F. E. Terman, 1st ed., 3rd impression,1943, published by McGraw-Hill Book Co., Ine., pp. 398, 399 and 400.

